We are studying the role of cell surface carbohydrate-binding proteins in a number of model systems. These include cellular slime molds, teratocarcinoma stem cells and fibroblast cell lines. In slime molds galactose-binding lectins have been identified and purified. Attempts are underway to identify the complementary cell surface receptors to which these lectins bind. A wide variety of evidence supports a cell adhesion function for the lectin-receptor complex. In teratocarcinoma cells and fibroblasts, there are cell surface binding components that recognize mannose-rich oligosaccharides. These components are identified as mediators of rosette formation between the tissue culture cells and certain species of erythrocytes. Preliminary evidence suggests that the teratocarcinoma lectin-like component may mediate cell cohesion. Purification of these components is planned.